Question

Answer 1

a)A=\(\dfrac{2.2}{1.3}.\dfrac{3.3}{2.4}.....\dfrac{20.20}{19.21}\)

A=\(\dfrac{2.3....20}{1.2....19}.\dfrac{2.3....20}{3.4....21}\)

A=\(20.\dfrac{2}{21}\)

A=\(\dfrac{40}{21}\)

Answer 2

a) Ta có: \(A=\dfrac{2^2}{1\cdot3}\cdot\dfrac{3^2}{2\cdot4}\cdot\dfrac{4^2}{3\cdot5}\cdot...\cdot\dfrac{20^2}{19\cdot21}\)

\(=\dfrac{2\cdot3\cdot...\cdot20}{1\cdot2\cdot...\cdot19}\cdot\dfrac{2\cdot3\cdot...\cdot20}{3\cdot4\cdot...\cdot21}\)

\(=20\cdot\dfrac{2}{21}=\dfrac{40}{21}\)